The present invention relates to a measuring unit for a weight-stack gym machine. The unit can be effectively used to measure the static and dynamic (or training) parameters connected with the load that can be lifted by a user performing an exercise.
For the measurement of these parameters, known systems include devices of an electromechanical and mixed electromechanical and optical type. Of these, the ones described in the following patent documents are worthy of note: patent application PCT WO 87/05727 filed in the name of the American company Physio Decisions, Inc. with priority date Mar. 10, 1986; U.S. Pat. No. 4,817,940 granted to the American company Fike Corporation, with priority date Apr. 4, 1986, and U.S. Pat. Nos. 5,655,977 and 5,785,632 granted to Integrated Fitness Corporation with priority dates Jul. 7, 1994 and Mar. 7, 1997.
Since experts in the trade are well aware of the teachings of these documents, the text which follows will only describe those aspects which evidence the drawbacks of the measuring units disclosed therein.
Firstly, it should be noted that all the above mentioned documents refer to gym machines where the load unit has a plurality of weights with a given thickness and slidably mounted on vertical bars. The weights can be lifted vertically by the user through a load unit comprising a bar, normally called through bar which goes through a vertical hole made in the middle of all the weights. Each weight also has a transversal hole made centrally in its side and the through bar has a plurality of transversal holes distributed along its length equally spaced according to the thickness of the weights so that when the weights are at rest, each of the holes in the through bar is aligned with the corresponding hole in each of the weights. The user selects the load to be lifted while the weights are at rest, supported by the frame, by inserting a transversal pin through one of the weights and into the corresponding hole in the through bar.
The above mentioned documents described measuring units equipped with an electrical position transducer, usually called xe2x80x9cencoderxe2x80x9d. This instrument normally includes a processor to which a rotary element is electrically connected in such a way that its angular position can be measured instant by instant. Thus, used in a weight lifting device having a flexible cable, it can keep track of the current position of the weight to be lifted relative to a reference position.
Document U.S. Pat. No. 4,817,940 describes a direct readout, digital encoder where a mechanical transmission pulley used to lift the weights has a plurality of holes made in it, the holes being equally spaced around the axis of rotation. The pulley is located between a light emitter and a light receiver. The alternation of light and dark pulses or a permanent dark signal provide the information used by the control unit to track the position of the load being lifted.
Document PCT WO 87/05727 is the first document which suggests the use of a xe2x80x9cwire encoderxe2x80x9d. This instrument, which comprises a tachogenerator and an automatic cable reel whose cylinder is coaxial with the axis of the tachogenerator, is connected to an electronic control unit that processes the position signal provided by the encoder and combines it with a time signal to provide as its output the speed and acceleration of the through bar while the machine is being used. The combination of this information, which is necessarily recorded by the control unit, and the values of speed and acceleration enable the control unit to calculate the dynamic parameters such as, for example, the instantaneous power exerted by the user and the total energy used at the end of the exercise. In this case, the encoder is connected to the weight stack and, in particular, to the pin used to select the load to be lifted. Thus, the detecting device permits measurement of the load selected by the user when the weights are at rest, with reference to the initial position of the pin relative to an initial encoder reference, that is, before the exercise starts.
In documents U.S. Pat. Nos. 5,655,997 and 5,785,632, the encoder wire is connected to the weight at the top of the weight stack and an optical device having the function of a switch permits calculation of the total thickness of the weights lifted by the user. The interruption of a light beam by the weights tack and the subsequent return to a continuous light beam condition, combined with the measurement of load movement by the encoder, enables the control unit to calculate the total load lifted.
Each of the measuring devices described in the above mentioned documents has drawbacks, some of which are common to more than one device.
Firstly, in the measuring devices equipped with wire encoder (PCT WO 87/05727, U.S. Pat. Nos. 5,655,977 and 5,785,632), the main disadvantage is the fact that the devices which define the change between the static position (where the number of weights selected, that is, the load, is measured) and the dynamic position (corresponding to the movement of the weight pack selected by the user) do not guarantee constant, reliable operation. For example, photocells may be blacked out by dust or they may move out of position as a result of the vibrations which are always present on machines of this kind. That means the state of the system must be periodically checked in order to prevent failure while an exercise is being performed.
The device described in document U.S. Pat. No. 4,817,940 is also negatively affected by wear since the load to be lifted acts directly on the pulley that constitutes the encoder which, in turn, transmits the stress to a pin supported by the frame. Further, in a measuring device based on an encoder of this kind, the static load must be set by the user and only on the basis of this information can the control unit calculate the training parameters. Consequently, incorrect programming by the user may result in the parameters being calculated inaccurately.
Moreover, although the encoder described in document WO 87/05727 is sufficient to measure the total lifted load and the training parameters, in patents U.S. Pat. No. 4,1817,940, U.S. Pat. No. 5,655,977 and U.S. Pat. No. 5,785,632, the calculation of the training parameter is performed by two separate devices. As is known, the duplication of the devices negatively affects the efficiency of the machine because the problems of one measuring device combine with those of the other to double the operating problems of the machine as a whole. Furthermore, the electronic control unit forming part of the measuring device must have two inputs for the signals corresponding to the static load and the training parameters.
The aim of the present invention is to provide a measuring unit for a weight-stack gym machine that is not subject to the drawbacks described above.
In particular, the present invention has for an object to provide a measuring unit for gym machines that permits automatic calculation of the parameters relative to the movement of the weights which form part of the training load, thus obviating problems due to wear, and using reliable measuring elements which can be retrofitted on existing machines without particular technical problems tending to radically modify the computing components of the machine.
Accordingly, the present invention provides a measuring unit for a weight-stack gym machine.